A biosensor is a device that measures the presence of various chemical components in a sample deposited in a biosensor cell. For example, a biosensor may be used to measure the amount of glucose present in a sample of blood. Generally, the biosensor cell includes a pair of conductors, e.g., gold and palladium, configured to receive a sample therebetween. Typically, the biosensor generates an electrical signal that is proportional to the amount of a certain component, e.g., glucose, in a sample, which is assumed to have a certain volume. If the sample is too small/large, however, the electrical signal will indicate a concentration which is lower/higher than the actual concentration of the component in the sample, resulting in the potential for improper diagnosis and treatment. Accordingly, methods and apparatus for determining the adequacy of a biological sample are useful.
One method for determining the adequacy of a sample within a biosensor cell is through the use of electric sensors. The electric sensors are conductors that detect the flow of electricity. In this method one or more detection conductors are positioned at different locations throughout the biosensor cell. When the sample comes in contact with a detection conductor, the detection conductor will conduct electricity, thereby indicating the presence of the sample at the location. Electronic circuitry can then be used to determine whether an adequate sample has been deposited into the biosensor cell based on the number of detection conductors that conduct electricity. This method has several drawbacks. First, several detection conductors are required in addition to the two existing parallel plate conductors of the biosensor cell. Second, an error is introduced if the sample touches a detection conductor without filling the area of the conductor completely. Third, this method is not able to compensate for bubbles trapped within the sample, which reduces the volume of the sample.
Another method for determining the adequacy of a sample applied to a biosensor cell is through visual confirmation of the sample volume. In this method, the user of the device visually inspects the sample within the biosensor to determine if a sufficient sample has been applied to the biosensor. This method relies on a subjective determination of the volume of a sample and is, therefore, prone to errors. This is especially problematic when the biosensor is used to measure chemical components associated with certain diseases, such as diabetes, that cause decreased visual acuity in the user.
The prior art methods used to determine the adequacy of a sample result in the test being performed only if the sample volume is within a narrow range. If the sample volume is outside of this range, the test is aborted. This “go/no-go” method of using biological samples, which relies on the sample volume being within a narrow range, results in wasted time and samples for samples outside this narrow range.
Therefore, there is a need for apparatus and methods to accurately determine the volume of a sample within a biosensor cell and to determine chemical component concentrations for a wide range of sample volumes. The present invention fulfills this need among others.